Classic and desmosomal cadherins are ubiquitous transmembrane adhesion receptors of epithelial cells. While significant progress has been made toward understanding classic cadherin adhesion, the mechanisms of adhesion by desmosomal cadherins have been poorly studied. Two factors - the complexity of desmosome cadherin composition and the insolubility of desmosomes - have hampered direct examination of protein-protein interactions in these structures. However, significant progress in understanding classic cadherin adhesion as well new assays that we developed have enabled us to address the question of cadherin-cadherin interactions in desmosomes on a more sophisticated level. The key Specific Aim of this application is the development of a site-specific cross-linking assay that is able to monitor intercadherin interactions in desmosomes. Such an assay is essential for clarifying many open questions about the mechanisms of desmosome formation. Among them are the following: (i) whether desmosomal cadherins are able to produce strand dimers; (ii) whether these dimers are heterodimers, homodimers, or both; (iii) whether this dimerization process can be reproduced in vitro or if it can proceed only in living cells within desmosomes; (iv) whether intracellular desmosomal proteins regulate extracellular adhesive interactions; and (v) whether desmosomes have a specific lateral alignment of desmosomal cadherins. Our previous experiments with classic cadherins provide a clear blueprint for such a study and indicate that this project is feasible. This application outlines a project to resolve a very difficult-to-study but critical aspect of cell-cell adhesion - the protein-protein adhesive interactions in desmosomes. Desmosomes are major adhesion structures in the epidermis that glue together keratinocytes. Despite their significance, it is not known how desmosomes form the tight, ordered and dynamic adhesive links between epidermal cells. Understanding this question is necessary for elucidating the mechanisms of severe human blistering skin diseases, including pemphigus foliaceus and pemphigus vulgaris. Furthermore, such knowledge will specify targets for compounds that decrease cohesion between epidermal cells. These compounds may have applications in wound healing and in promoting fast delivery of other drugs or vaccines throughout the skin. Since desmosomes are involved in intracellular signaling, the manipulation of their adhesive interactions may present a new avenue for modulating intracellular signals in order to correct hyperproliferation, abnormal differentiation and other skin abnormalities. [unreadable] [unreadable] [unreadable]